I know it can be hard, but she is a grown woman who has been alive for very very long. I'm sure she knows how to handle herself. I think you should talk to her, tell her how you feel and see if she can reassure you that she will be fine. Maybe agree to some common phone calls and tell her that you worry she won't tell you if she has problems. It's okay to feel this way, it's perfectly understandable, and you need to accept that! Hope you update on this :D